Electric fuse



April l0, 1934.` A. J. BowlE 1,954,037

ELECTRIC FUSE Filed March 18, 1931 Patented Apr. 10, 1934 UNITED STATES PATENT OFFICE 4Claims.

fuse wire is necessarily of small diameter.'

Hence, regardless of the fact that the fuse wire of small diameter may or may not be surrounded with a powder of some kind, air is present in and about the particles of powder or space adjacent to the fuse'wire.- Therefore if this fuse wire of small diameter be raised to a sufficiently high potential, the previously mentioned adjacent air will be over-stressed in the concentrated electrostatic ileld surrounding the small wire, with resulting corona discharge and radio interference.

This over-stressing of the dielectric eld adjacent to a small conductor can be prevented either by surrounding the small conductor with a metal tube in electrical contact with such conductor and of suiicient diameter to prevent the 'over-stressing of the dielectric, or by increasing the diameter of the conductor to such an extent that at the potential at which the conductor will normally be operated, the air adjacent to the conductor will not be over-stressed and corona eect will not be present.

In the ordinary types of construction the terminal ferrules at the ends of the insulating tube are of sufficient length to shield the small diameter fuse wire, but should there be in any particular design a ferrule of insuiiicient length properly to shield the small fuse wire I would extend the ferrule to such dimension as properly to shield the said wire.

Fuses of this nature are generally enclosed in an insulating tube for mechanical protection as well as for necessary blow-out action. The conductor within the tube, if unshielded by special or regular construction of the tube, I make preferably with an exterior diameter larger than would otherwise obtain. This can be effected in a number of different ways, such as winding fuse wires over a supporting insulating core, or the use of a hollow conductor. If the former method is used, it is unnecessary to have the surface entirely covered, provided a fair distribu- 55 tion of the conductors is arranged so as to give (Cl. 20o-131) in effect a larger conductor which will prevent radio disturbance. One of the objects of this invention is to provide a fuse element or conductor of such a nature.

While the fuse may continue the full length of the tube, I prefer to have a relatively short fusible section at one end of the fuse tube and an extension within the tube of much larger section. The small section may be shielded by the ferrules from radio disturbance, but the larger section, due to increased diameter, will preclude radio trouble, otherwise inevitable.

As the extension of the fuse is of conducting material, it must either be volatilized or expelled from the tubewhen the fuse blows. It is advisable to have this material expelled, together with any other material within the tube at the time the fuse blows. Hence, the material comprising the extension of the fuse element in the tube should be of light, flexible construction, including the supporting member which may be ejected when the fuse blows. The fuse extension is preferably attached to the blow-out cap, so that it will be positively pulled out of the tube when the blow-out cap is ejected.

Another function of this invention is to obtain the necessary power for blow-out of the fuse, by providing special material which will be gassifled by the arc resulting when the fuse blows, hence giving a powerful blow-out action.

Figure 1 shows a longitudinal section of the fuse. Figure 2 shows an end View thereof. Figure 3 shows a cross-section of the fuse conducting element. Figure 4 shows a longitudinal projection of a hollow fusible element, and Figure 5 shows 90 a cross-section of the same. Figure 6 shows a longitudinal projection of a different type of element, and Figure 7 a cross-sectional view of the same.

Figure 8 is a longitudinal section of a. fuse with 95 a hollow conducting fuse extension element with the tube powder filled on the outside. Figure 9 is a cross-section of the design shown in Figure 8.

l is a fuse tube with inner liner tube 2. 3, 4 are ferrules for conveying current from the tube. 100 5 is a screw-nut cap tor closing end of the fuse tube. 6 is a disc to which the fuse 7 is soldered.

8, 9 are pieces of material which may be readily volatilized, such as metallic lead, tin or zinc or any alloys of these metals. 10 is a fuse conductor 105 wound on core 11. 12 is an end cap with screw connection 13. 14 is a blow-out cap which contacts with cap 12 and with the ferrule 3. 15 is a small asbestos sleeve.

7 is the fuse link proper. 8, 9 are buttons which u( will be gassifled when the fuse blows. The arc formed will hence provide pressure for expelling forcibly cap 14, cap 12, and elements 10 and 11. The conducting element 10 may be made of line copper wire which will not normally melt on blowing of the fuse, but will be ejected as a whole; though this element may be made of fusible material, generally of a greater section of metal than that of the fuse 7. Core 11 may be asbestos, preferably flexible and insulating.

Core 11 is partly covered by conductor 10 wound spirally over it. This very much increases the normal diameter of conductor 10 and results in a consequent freedom from corona effects. Fuse 7, although of very small diameter, generally is shielded by the ferrule 4, so that the fuse wire being ofsmall diameter is shielded electrostatically and will not be the source of corona discharges, but the increased equivalent diameter of the outside of 10 will in itself act to prevent corona.

Figure 4 shows an alternative construction` for elements 10 and 11, being a hollow conducting tube 16, which will be expelled when the fuse blows. This is supported on core 11.

Figure 6 is a longitudinal view, and Figure 7 a cross-section of an alternative construction for items 10 and 11, wherein 17 isthe conducting element and 18 is a central core supporting the same. The central core may be any type of material, preferably light and of suicient mechanical strength to servaas a support for the conducting material 17, which may be, for example, of tin foil, metallic paint, or any other form of conductor. 17 may be electrically connected to the fuse circuit at one or at both ends of the tube. It is very desirable, for the best results, that the conductor 17 be made in the form of a closed tube, since even if it is constructed with a general circular shape and not entirely closed, the edges of the conductor are liable to cause radio disturbance which would be eliminated if the conductor were made into a perfect cylinder.

19 is a conductor, preferably located within the material 18, of ample section to carry the current. If conductor 19 is employed, conductor 17 may be made extremely light, the effect being to do away with corona effects.

The ejection of the entire fuse material is greatly improved by building up a pressure Within the fuse tube sufficient to overcome the friction between cap 14 and ferrule 3. This is helpful to eject properly the central core and conductor l0, as well as the end caps. To get proper blowout renders advisable the closure of the fuse at both ends to thev atmosphere to allow building up sufficient pressure to cause effective expulsion. It is of advantage to have the end cap continue back up the fuse tube, as thereby cap 14, fitting closely over tube l, is subject to a pressure within the tube over a considerable distance, acquiring a velocity like that which would obtain with a projectile in the barrel of a gun.

. Another important feature of this construction is that the conducting path is down through the fuse tube and back up the outside of the fuse tube, making a return circuit which is interrupted in two places when the fuse blows.

Referring to Figure 8, the fuse conductor 17 within the fuse tube conveys current from the fuse to the cap'12 and thence to ferrule 3. Conductor 17 may be of material which will not be readily volatilized when the fuse blows. If attached mechanically to cap 12 and blow-out cap le, it will be ejected from the tube when the fuse blows. It is preferably made of light material, rendering it flexible when discharged from the fuse. The interior of conductor 17 is sealed by light gaskets 20, 2l, which serve to prevent the entrance of granular insulated filling material 22 to the interior ofthe tube. When the fuse blows, the pressure will break down these pieces 20, 21 and allow the ejection of the conductor 17, together with the lling material from within the tube. If desired, gasket 21 may be omitted.

The fuse will consist of a small section adapted to function in the customary manner generally in series with a conducting element of larger section which will either melt on blowing of the fuse, or be ejected from the tube when the fuse blows. In any event, the conducting element in the claims refers to the metal conductor either composing the fuse or in series with the fuse which will hence constitute an open gap when the fuse blows and functions.

In general, these two sections will be disposed in series within the fuse tube.

What I claim is:

1. In a high tension fuse, an enclosing tube, ferrules on said tube for conducting current to and from said tube, a short fuse element within said tube electrically connected to one of said ferrules, a mass of volatilizable metal adjacent to said fuse element adapted to be Volatilized when said fuse element blows, and a conductor attaching said fuse to the second ferrule on the opposing end of said tube through a blow-out cap normally closing the fuse tube to the atmosphere, said blow-out cap makingfrictional contact with said second ferrule, said cap conveying current from the inside of said tube back up the outside of said tube to said second ferrule.

2. In a high tension fuse, an insulating fuse tube, a pair of ferrules mounted on said tube, a closure closing one end of said tube to the atmosphere, means for closing the other end of said tube, a short fuse element within said tube, a mass of metal readily volatilizable adjacent to said fuse element, a conductor between said fuse element and one of said ferrules, and a blow-out cap making frictional contact with said second last-mentioned ferrule, said blow-out cap conducting the current from the interior of said fuse tube back up the exterior of the tube to said second ferrule, the said blow-out cap being adapted to be expelled from said fuse tube when said fuse element blows.

3. The combination in a high tension fuse of a composite fusible element consisting of a relatively short small diameter section in series with a relatively longer and larger diameter section, the smaller diameter section being below the corona forming limit for the diameter of the fusible element and rated voltage of the fuse while the larger diameter section is above the corona forming limit for the diameter of the fusible element and rated voltage of the fuse, means for electrostatically shielding the said small diameter portion of the said fusible section to counteract its tendency to form corona at rated voltage of said high tension fuse, a fuse structure consisting of an insulating fuse tube, a pair of ferrules mounted on said tube, a closure closing one end of said tube to the atmosphere, means for closing the other end of said tube, a short fuse element within said tube, a mass of metal readily volatilizable adjacent to said fuse element, a conductor between said fuse element and one of said ferrules, and a blow-out cap making frictional contact with said second last-mentioned ferrule, said blow-out cap conducting the current from the interior of said fuse tube back up the exterior of the tube to said second ferrule, the said blowout cap being adapted to be expelled from said fuse tube when said fuse element blows.

4. In a high tension fuse a fuse tube, terminals .for said fuse tube for conveying current to and from said tube, the rst of said terminals being mounted externally to said tube and backward up the tube from the end thereof, a fusible element of relatively small cross-section attached to the second ferrule on said tube, a conductor 

